docs: def validate(self, corpus):
          """
          Perform the validation on the given corpus.
  
          Args:
              corpus (Corpus): The corpus to test/validate.
  
          Returns:
              InvalidUtterancesResult: Validation result.
          """
          invalid_utterances = {}
  
          for utterance in corpus.utterances.values():
              duration = utterance.duration
              ll = utterance.label_lists[self.label_list_idx]
  
              # We count the characters of all labels
              transcription = ' '.join([l.value for l in ll])
              num_chars = len(transcription.replace(' ', ''))
  
              char_per_sec = num_chars / duration
  
              if char_per_sec > self.max_characters_per_second:
                  invalid_utterances[utterance.idx] = char_per_sec
  
          passed = len(invalid_utterances) <= 0
          info = {
              'Threshold max. characters per second': str(self.max_characters_per_second),
              'Label-List ID': self.label_list_idx
          }
  
          return base.InvalidUtterancesResult(passed, invalid_utterances, name=self.name(), info=info)